Seasonal Vegetables (& fruit) are food goods that are only available throughout certain months of the year, but now due to globalisation many fruit and vegetable are available at all times of year. For example in the UK you can buy strawberries in the coldest month of winter, and they are imported from abroad.
Vegetables that grown in summer are usually called "summer vegetables" or "seasonal vegetables". You can use the following terms in the following ways:
-I like seasonal vegetables. It's sad that they aren't there all the time.
-Tomatoes are an example of summer vegetables.
夏に育つ野菜のことは「summer vegetables（夏野菜）」や「seasonal vegetables（季節の野菜 / 旬の野菜）」と呼ばれます。
以下、例文です。
I like seasonal vegetables. It's sad that they aren't there all the time.
（季節の野菜が好きです。常に食べられないのが残念です。）
Tomatoes are an example of summer vegetables.
（トマトは夏野菜の一つです。）
When we talk about vegetables being in season in one of the 4 seasons (spring, summer, autumn,winter) you simply say 'summer/spring/autumn/winter vegetables'
examples of summer vegetables are corn, cucumbers, peas
1. "Summer vegetables"
The adjective in this sentence is 'summer' which shows that the vegetables are in season during the Summer months,
2. " Seasonal vegetables"
Seasonal vegetables are vegetables which grow in one of four seasons (Autumn, Winter, Summer, or Spring). Seasonal vegetables include summer vegetables. The adjective in this example sentence in the word 'seasonal', with the noun being 'vegetables'.
3. "Summer produce"
Similar to the first example sentence, summer produce refers to food which is in season during the summer. The difference, however, is that the noun 'produce' can include things other than vegetables, such as fruit or grains.
If you want to talk about vegetables which grow during the summer months, then you can just describe them as 'summer vegetables.' Of course, most summer vegetables are not in season all summer - but only for a perhaps a short period of time such as 1 or two months, so it is probably more helpful if you talk in terms of the month or months that such vegetables are available.
"The strawberry season starts in May in the UK."
The copntext is always important. If it is summetime an you are talking about summer vegetables, then the description 'fresh vegetables' is obviously quite adequate.
夏の時期に育つ野菜について言いたいなら、シンプルに 'summer vegetables'（夏野菜）と表せます。もちろん、ほとんどの夏野菜の旬は一カ月とか二カ月で、夏の間ずっとというわけではありません。ですから、それらの野菜を食べられる「月」を言ってあげた方がより親切だと思います。
"The strawberry season starts in May in the UK."
（イギリスではイチゴの季節は5月に始まります）
文脈は常に重要です。夏の時期に夏野菜について話すなら、'fresh vegetables'（新鮮な野菜）で十分に伝わります。
日本 
イギリス 
南アフリカ 
